Patent document EP-A-0 557 943 describes phosphazene compounds that can be cured by radical polymerization, the polymerization of which is initiated by adding initiators or by electron radiation. Patent document EP-A-0 368 165 describes curable resin compositions that contain a curable phosphazene compound and a pentaerythritol acrylate compound and/or a bis(4-acryloxydialkoxpheyl)alkane compound mixed together. These known phosphazene derivatives have one or more of the following drawbacks. They tend to polymerize prematurely, so that stabilizers have to be added. High storage temperatures have to be avoided, which in turn results in drawbacks for shelf life and choice of conditions for synthesis, yields, and absence of chlorine. Radical polymerization is inhibited by atmospheric oxygen and thermal curing in particular frequently leads to incompletely hardened surfaces. Curing often occurs very slowly and leads to products that discolor with time. During the curing, severe shrinkage frequently occurs that leads to deterioration of behavior and cracking. So, such phosphazene derivatives, or their mixtures pursuant to the state of the art, cannot be used for many applications, including use as binders for paints and coatings in particular.
The invention makes available new phosphazene derivatives that avoid these drawbacks of the state of the art and provides polymerizable products with improved properties. In particular, it is desirable to avoid a radical mechanism for polymerization of the phosphazene derivatives.
In one aspect, the invention provides polymerizable phosphazene derivatives with the following structural formula EQU [--NP(A).sub.a (B).sub.b --].sub.x
wherein the groups A and B are bonded to phosphorus atoms through --O--, --S--, --NH--,or --NR-- (R=C.sub.1 -C.sub.6 alkyl); A contains at least one vinyl ether group of the general formula Q--O--CR'.dbd.CHR" and/or styrene ether group of the general formula ##STR1## wherein R' and/or R" stands for hydrogen or C.sub.1 -C.sub.10 alkyl; B stands for a reactive or nonreactive hydrocarbon group optionally containing O, S, and/or N, and optionally containing at least one reactive group; Q is an aliphatic, cycloaliphatic, aromatic, and/or heterocyclic hydrocarbon group, optionally containing O, S, and/or N; a is a number greater than O; b is 0 or a number greater than 0 and a+b=2; x stands for a whole number that is at least 2; and z stands for 0 or 1.
The open bonds in the formulae above indicate either joining into a ring with alternating atoms of N and P, or a bonding to groups A or B or the usual catalyst or initiator molecule groups. The later, for example, can be found in Makromol. Chem., 183; 1833-1841 (1982) and Makromol. Chem., 183; 1843-1854 (1982) or can be those of Lewis acids, SbCl.sub.3, AlCl.sub.3, or sulfur compounds.
The phosphazene derivatives of the invention can contain two or more different vinyl ether groups and/or both vinyl ether groups and styrene ether groups in one molecule. The phosphazene derivatives of the invention, which can be polymerized cationically at least when substituted by vinyl ether groups, and whose polymerization can be initiated by acids, have one or more of the following advantages over known phosphazene derivatives: complete substitution of the phosphazene and thus absence of chlorine can be achieved in high yields; oxygen does not inhibit the curing of the phosphazene derivatives of the invention; even thin coatings are completely cured in the presence of atmospheric oxygen, which makes thermally initiated curing possible in particular; they have no tendency to discolor the polymerized product; they are ordinarily less viscous and therefore more suitable for low-solvent application; and they have less tendency to shrink.
All of these properties make the polymerizable phosphazene derivatives of the invention suitable as curable binders for paints, coatings, fillers, mastics, adhesives, moldings, or films, especially as binders for paints and coatings. For example, they can be used advantageously as binders in transparent coatings for exterior varnishing, or for varnishing interior wood trim in motor vehicles. They can also be used in transparent coatings for polycarbonate headlight diffusion lenses or the like. The usual additive substances such as initiators, pigments, leveling agents, pigments, UV stabilizers, fillers, and the like, can be added to formulations containing the polymerizable phosphazene derivatives of the invention.
The structural formula for the phosphazene derivatives of the invention, shown above, states that they are necessarily at least partially substituted on the phosphorus atoms by groups that contain at least one vinyl ether group and/or styrene ether group, as shown and described. Therefore, the substituent B may be, but does not have to be, present in the phosphazene molecule (i.e., b may be 0).
The phosphazene derivatives of the invention can be cyclic or acyclic compounds, which have a structural skeleton of alternating nitrogen and phosphorus atoms in every case. The cyclic compounds in which x stands for 3 or 4 and which, therefore, consist of 6- or 8-membered rings are preferred. The 6-membered ring, in which x stands for 3, is particularly preferred.
Q is a spacer group that is bonded to a phosphorus atom through an oxygen atom, a sulfur atom, an NH group, or an NR group, and that has at least one vinyl ether group and/or styrene ether group, in which R' and R" have the meanings given above, at its free end and/or as a side group. R' and/or R" in these groups are preferably hydrogen, methyl, or ethyl, and preferably are hydrogen.
Compounds especially preferred according to the invention are those with the general structural formula ##STR2## wherein Z and Z' are the same or different and each stands for --O--, --S--, --NH, or --NR-- (R=C.sub.1 -C.sub.6 alkyl); Q stands for an aliphatic, cycloaliphatic, aromatic, and/or heterocyclic hydrocarbon group optionally containing O, S, and/or N; YH stands for an aliphatic, cycloaliphatic, aromatic, and/or heterocyclic hydrocarbon group optionally containing O, S, and/or N and/or optionally containing a reactive group different from a vinyl ether group or a styrene ether group; y is O or 1; x stands for a whole number from 2 to 20; and a, b, R', and R" are as defined above.
R in the above formulas is alkyl with 1 to 6 carbon atoms, preferably methyl or ethyl. In the last formula given above, Z and Z' are preferably --O--.
The spacer group Q and the YH group can have such structures that they control the properties of the phosphazene derivative. Thus, the Q and YH groups can have very diverse structures. Examples of such Q and Y groups can be found in German patent document DE-A-4 325 776. They are usually alkaline groups with various chain lengths, straightchained or branched, preferably with 2 to 20 carbon atoms, and especially with 2 to 6 carbon atoms, biphenylene, phenylene or oxyalkylene groups, or combinations thereof. In the case of oxyalkylene groups, they are preferably oxyalkylene groups with the formula --(CH.sub.2 -CH.sub.2 -0).sub.n, wherein n is 1 to 20, preferably 1 to 6. The spacer groups Q and Y can optionally contain substituents on this preferred structural formula, or can be interrupted by other groups. Examples of such substituents are ester groups, keto groups, OH groups, or NH.sub.2 groups. Examples of groups inserted into the alkaline chain in turn are ester groups, keto groups, urethane groups, or NH groups.
The YH group can be straight-chained or branched, and can consist of a reactive or nonreactive group or can contain a group that differs from the vinyl ether and styrene ether groups of the above formulas. Preferred reactive YH groups are or contain isocyanate groups, carboxyl groups, allyl groups, vinyl acetate groups, N-methylol groups, epoxide groups, glycidyl ether groups, acrylate groups, methacrylate groups, silyl groups (such as C.sub.1 -C.sub.6 alkoxysilyl or aceeoxysilyl groups), OH groups, or NH.sub.2 groups. The reactive groups can also be blocked in the usual way. The selection of the YH group, however, is not to be limited to the above enumerated groups.
The preferred phosphazene derivatives of the invention are those in which y is O or 1, i.e., those that are vinyl ether derivatives. In any case, they can be cured with cationic initiation using at least one acid. This can be done by direct addition of acid. Instead of this, initiators can be added to the formulation that split off acids when irradiated with UV light or electron beams or when the temperature is raised, which in turn then initiate the polymerization. If the molecule contains other reactive groups in addition to the vinyl ether groups, multicure procedures can be used, for example, combinations of thermal curing, curing by atmospheric humidity or atmospheric oxygen, and UV curing.
The phosphazene derivatives containing styrene ether groups of the invention are ordinarily polymerized in the usual way by a radical mechanism. Thus, optionally, either initiators that split off radicals when irradiated with UV light or in some other way are added, or radicals are generated without addition of initiator by, for example, introducing thermal energy or by electron irradiation. Anionic or cationic polymerization is also possible in certain cases.
The phosphazene derivatives pursuant to the invention can be prepared by reacting a chlorophosphazene with at least one compound of the general formula MA, alone or in combination with at least one compound of the general formula MB, or successively with MA and MB, in an inert solvent. In these compounds, A and B are as defined above and M stands for a hydrogen atom, an alkali metal, an alkaline earth metal, or a basic group. The basic group M, for example, can be a pyridyl group or a tertiary amino group such as a triethylamino group, or it can be a 1,8-diazabicyclo[5,4,0]undec-7-ene(1,5-5) group. It is preferred for M to be sodium. The compounds MA and MB can be obtained by reacting the compounds HA and/or HB with sodium hydride, sodium metal, or sodium hydroxide, for example, by the procedure of U.S. Pat. No. 4,775,732 (US-A-1 4 775 732).
In accordance with the above embodiments, the preferred compounds MA are those with the formula ##STR3## and the compounds MB are those with the general formula M--Z'--YH, wherein M, Z, Z', Q, Y, R', R", and y are as defined above.
The preferred process for preparing the phosphazene derivatives of the invention consists of using compounds MA and MB in which M is bonded to an oxygen atom, and thus Z and Z' stand for --O-- in the above preferred formulas for MA and MB. Examples of practical inert solvents in which the reaction is carried out are tetrahydrofuran, toluene, dimethyl sulfoxide, dimethylformamide, chloroform, methylene chloride, and pyridine. Suitable reaction temperatures are between 15 and 110.degree. C., preferably between 18 and 70.degree. C., with lower temperatures requiring longer reaction times. Depending on the temperature selected, it is desirable for the reaction times to be between 5 and 60 hours.